Although lithium is the primary treatment for bipolar affective disorders, its mechanism of action is unknown. However, results from this and other laboratories have identified two potentially important effects of therapeutically relevant concentrations of lithium after chronic administration to rats, impairment of second messenger formation (especially phosphoinositide hydrolysis) in brain, and enhanced responses to cholinergic agonists. Therefore, this proposal is designed to test several specific hypotheses as to the mechanism of action of lithium on these systems as well as studying basic modulatory mechanisms of second messenger production and acetylcholine metabolism. To test the hypothesis that chronic lithium treatment impairs phosphoinositide hydrolysis both in vivo and in vitro methods will be used. We have recently applied a new method which measures the endogenous unlabelled concentrations of inositol phosphates in rat brain regions after sacrifice by microwave irradiation and found after chronic lithium an 80% depletion of inositol trisphosphate and a reduced response to stimuli. Dose-response, time course, and interactions with specific agonists and antagonists will be carried out. In vitro measures of phosphoinositide hydrolysis will be carried out to more completely identify mechanisms of modulation of phosphoinositide hydrolysis. To test the hypothesis that chronic lithium treatment and other drugs, as antidepressants and glucocorticoids, alter the function of G-proteins, we will (i) apply Northern blot analysis using cDNA's for 5 G-proteins to measure mRNA concentrations, (ii) use monoclonal antibodies and immunoblot analysis to measure G-proteins, and (iii) measure ADP-ribosylation catalyzed by cholera toxin, pertussis toxin, and the endogenous ADP- ribosylation factor. To test the hypothesis that lithium potentiates cholinergic function, we will (i) use EEG recordings in rats treated with cholinomimetics and either lithium, which potentiates their actions causing seizures, or pertussis toxin, which also potentiates cholinomimetic function, and (ii) measure acetylcholine metabolism in vitro to identify modulatory effects of second messengers and the effect of lithium. To test the hypothesis that lithium impairs cyclic AMP production, but less so than phosphoinositide hydrolysis, the G-proteins associated with the cyclic AMP system are included in the studies given above and cyclic AMP concentrations will be measured after the same treatments used to measure inositol phosphate production.